In the present day, with the higher integration and downsizing of semiconductor elements, the amount of heat generated is ever increasing, and the problem of how to efficiently dissipate heat is becoming important. Additionally, circuit boards having a copper or aluminum metal circuit formed on the front surface of a ceramic substrate having high insulation properties and high thermal conductivity such as, for example, an aluminum nitride substrate or a silicon nitride substrate, and a copper or aluminum metal heat dissipating plate on the rear surface, are used as power-module circuit boards.
The typical heat dissipation structure of a conventional circuit board comprises a metal plate, for example, a base plate soldered by way of a copper plate, on the rear surface (heat dissipation surface) of a circuit board, and copper has been generally used for the base plate. However, with this structure, when a thermal load is applied to the semiconductor device, cracks caused by the thermal expansion coefficient difference between the base plate and the circuit board may occur in the solder layer, and as a result, the heat dissipation may be inadequate and cause problems such as malfunctions or damage to the semiconductor element.
Therefore, an aluminum-silicon carbide composite has been proposed as a base plate for making the thermal expansion coefficient closer to that of circuit boards. As the production method for the aluminum-silicon carbide composite for use in a base plate, a molten metal casting method involving pressurized impregnation of a molten aluminum alloy into a silicon carbide porous body (Patent Document 1) and a non-pressurized impregnation method involving non-pressurized penetration of a molten aluminum alloy into a silicon carbide porous body (Patent Document 2) have been brought into practice.
However, aluminum-silicon carbide composites have the problem that, when producing a heat dissipating component or the like as described above, high-precision shape working and screw-hole working is required, and in order to allow working, the compositing of the silicon carbide causes problems such as inferior workability and increased cost.
Therefore, in order to solve the above-mentioned problem, it has become customary to arrange beforehand to have the parts of the aluminum-porous silicon carbide molded body that are to be worked made out of an aluminum alloy, which excels in workability, and to perform shape working and screw-hole working by known metalworking methods.
[Patent Document 1] JP 3468358 B
[Patent Document 2] JP H5-507030 A